Water detection from downwash-induced optical flow for a multirotor UAV

Ricardo Pombeiro, Ricardo Mendonça, Paulo Rodrigues, Francisco Marques, Andre Lourenço, Eduardo Pinto, Pedro Santana, José Barata

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

7 Citations (Scopus)


Terrains of different nature exhibit distinct structural dynamics when exposed to wind due to their own intrinsic material composition. This translates into peculiar optical flow patterns that can be used to identify the terrain type. In this sense, this paper proposes an active vision-based water detection model that exploits the predictable optical flow patterns induced by the downwash effect of vertical take-off and landing Unmanned Aerial Vehicles (UAV). To determine whether a water surface is below the UAV, the system tracks the optical flow in the video feed captured by a downward-looking camera. Then, an histogram of optical flow orientation is built and compared against a model histogram, given the expected effect induced by the downwash effect. The histograms are compared and similarity between both histograms is used as the likelihood of the terrain as being covered by water The resulting classification can be used to guide the landing of the UAV or to produce cost maps supporting ground vehicles' safe navigation. The model was successfully validated on 20 videos acquired with an hexacopter while hovering above sandy, grassy, and water-covered terrains.

Original languageEnglish
Title of host publicationOCEANS 2015 - MTS/IEEE Washington
Place of PublicationNew York, USA
PublisherInstitute of Electrical and Electronics Engineers Inc.
ISBN (Electronic)978-093395743-5
Publication statusPublished - 8 Feb 2016
EventMTS/IEEE Washington, OCEANS 2015 - Washington, United States
Duration: 19 Oct 201522 Oct 2015


ConferenceMTS/IEEE Washington, OCEANS 2015
Country/TerritoryUnited States


  • Fires
  • Fire extinguishers
  • Ground vehicles


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